For a realistic simulation of images that change when the head position and head orientation of the observer changes, e.g. of panoramic image details shown on the night-vision goggles of a pilot, the observer's point of sight and thus his/her exact head position and orientation must be known for a precise calculation of the image detail that changes with the head movement. A magnetic field is generated in a real space in which the observer is seated, e.g. in the cockpit of an airplane or a helicopter, and a magnetic field sensor is attached to the head of the observer for sensing the magnetic field. The values measured by the magnetic field sensor represent a measure for the momentary head position or the momentary orientation of the observer's head in the magnetic field space and are referred to in the following as measuring position and measuring orientation.
A magnetic field sensor of this type operates without problems in the undisturbed, homogeneous magnetic field. However, the magnetic field of most magnetic field spaces is distorted by the presence of metal objects, for example the metal struts of a flight simulator cockpit. The measuring values output by the magnetic field sensor thus deviate from the true position and orientation of the magnetic field sensor in the real magnetic field space. In the distorted magnetic field space, the measuring values output by the magnetic field sensor must therefore be corrected to obtain the actual or so-called true position and true orientation of the magnetic field sensor, which is indispensable for a precise and realistic simulation of the image details.
A number of different methods are known for correcting the false measuring values output by the magnetic field sensor that is located in the distorted magnetic field. However, these methods do not yield sufficient and satisfying results, at least not for sight simulation. With one known method, the correlation between the true position and true orientation of the magnetic field sensor and the values measured by this sensor is determined experimentally and stored in a calibration table. In a pre-processing step, the calibration space is scanned and an approximation is used to obtain the associated, real position values by using the calibration table and interpolating the position values in the real magnetic field space. During the measuring phase, a trilinear interpolation is performed between the actually measured positions and the real position values to obtain the true position of the magnetic field sensor. (Volodymyr Kindratenko “Calibration of electromagnetic tracking device,” Virtual Reality, Research, Development, and Applications, Vol. 4, 1999, pages 139–150, with reference to Raab, Blood, Steioner, Jones: “Magnetic position and orientation tracking system”; IEEE Transactions on Aerospace and Electronic Systems 1979, 15(5), pages 709–718). This method is based on the assumption that the magnetic field interference in a space is linear, which is true only in exceptional cases.
Thus, there is a need for a robust method for determining the true values for position and orientation of a magnetic field sensor from the measuring values output by the magnetic field sensor. The method should provide results that are usable for sight simulation even in magnetic fields with heavy distortion or interference.